In grease gun applications, lubricant is loaded into the barrel of the gun using a variety of different methods. In a first method, the barrel of the gun is loaded with lubricant using one of several bulk loading techniques. In one such technique, referred to as pressure loading, lubricant is pumped into the barrel through the dispensing head of the gun from a source of lubricant under high pressure. In another bulk loading technique, referred to as suction loading, the follower assembly of the gun is retracted manually to create a suction pressure in the barrel which draws lubricant from a suitable source into the barrel. In a third technique, bulk loading is accomplished simply by hand-packing the barrel with heavy lubricant.
In addition to bulk loading, the barrel of the gun can be loaded with a lubricant cartridge that consists of a sleeve open at both ends and pre-packed with lubricant. With the pump head end of the lubrication gun removed, the cartridge is slid into the gun barrel and the end replaced.
With this background, it has proven difficult to construct a follower assembly that will adequately seal with respect to both the inner diameter of the gun barrel, in the case of bulk loading, and the inner diameter of the cartridge, in the case of cartridge loading, since the barrel and cartridge have different inner diameters. In the past, this problem has been approached in a variety of ways, none of which have been totally satisfactory.
U.S. Pat. No. 4,247,023 describes a follower assembly that seals against the barrel of the lubrication gun or against the smaller diameter of a lubrication cartridge positioned in the barrel. During manual priming, a follower rod moves the follower body forward by engagement between a projection on the rod and a back-up plate behind the follower body, and rearward by engagement of a washer carried by the rod with the front of the follower body.
U.S. Pat. No. 3,038,768 describes a follower packing adapted for use in a grease gun loaded either with bulk grease or grease in a cartridge. The follower is adapted for easy entry into a cartridge and to make a tight seal against the cartridge to prevent by-passing of grease around the follower rod.
The devices described in the above patents have drawbacks. For example, in U.S. Pat. No. 4,247,023, the use of an engagement washer on the follower rod disrupts the sealing surface between the follower rod and seal assembly when the user is pulling the grease follower in a rearward direction away from the pump head to prepare the grease gun for refill. Eventually, after repeated applications, this disruption causes by-pass of grease from the front portion of the follower assembly to the back portion of the follower assembly. This is an undesirable because any grease in the back portion of the follower assembly is wasted.
In the case of U.S. Pat. No. 3,038,768, the sealing ability of the follower seal denoted 53 against the grease tube denoted 1 or cartridge denoted T is limited when moving the grease follower rod forward for priming purposes. Users complain there is by-pass of grease between the follower seal and the grease tube or cartridge causing undesirable situations as grease is wasted.
Another grease gun of conventional design is shown in FIG. 1. The gun has a follower rod 1, an elastomeric seal 3 forming a cavity, a rear support 5 and a two-piece front support 7. The rear support 5 is not fastened to the elastomeric seal 3 and is only retained by a spring 15 against the elastomeric seal. When there is a need to prime the grease gun after loading of grease, an engagement pin 17 on the follower rod 1 is positioned in contact with a back surface 21 of the front support. A pushing force on the follower rod 6 acts against the back surface 23 of the elastomeric seal 3, causing distortion of the seal. This distortion allows grease from the lubricant chamber to by-pass the seal.
There is a need, therefore, for a lubrication gun having a follower assembly providing a more effective seal against the inside surface of the barrel, in the case of bulk loading of lubricant in the barrel, and against the inside surface of a cartridge of grease in the barrel, in the case of cartridge loading.